Hurricane ISABEL

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HURRICANE ISABEL DISCUSSION NUMBER 35
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT SUN SEP 14 2003
THE AFTERNOON PLETHORA OF RECON WIND AND PRESSURE DATA INDICATE THAT
ISABEL REMAINS BARELY BELOW CATEGORY 5 INTENSITY. AIR FORCE RESERVE
HURRICANE HUNTERS MEASURED 700 MB FLIGHT-LEVEL WINDS OF 150 KT...OR
135 KT SURFACE EQUIVALENT...IN THE NORTHEAST QUADRANT OF THE
EYEWALL...WHILE A NOAA HURRICANE HUNTER DROPSONDE REPORT INDICATED
171 KT AVERAGE WINDS IN THE LOWER 150 METERS...OR 139 SURFACE WIND
EQUIVALENT. BASED ON THIS INFORMATION...ISABEL IS BEING MAINTAINED
AT 135 KT. THE OUTFLOW PATTERN REMAINS VERY IMPRESSIVE AND HAS
CONTINUED TO EXPAND.
THE INITIAL MOTION ESTIMATE IS 290/11. THERE IS NO SIGNIFICANT
CHANGE TO THE PREVIOUS 2 FORECAST TRACKS OR REASONINGS. RECON FIX
POSITIONS HAVE BEEN COMING IN RIGHT ON TRACK AND THE LATEST 12Z NHC
MODEL GUIDANCE CONTINUES TO CONVERGE ABOUT THE PREVIOUS 2 FORECAST
TRACKS. THE LATEST GFDL RUN HAS CONTINUED ITS WESTWARD SHIFT IN THE
FORECAST TRACK AND THE 96-120H TRACK IS AT LEAST 90 NMI WEST OF THE
00Z TRACK. ONE DISTURBING BIT OF INFORMATION IS THAT THE 12Z
UKMET... GFS...GFDL...AND CANADIAN MODELS DID NOT ANALYZE THE 500
MB HEIGHT AND WIND FIELDS TO THE 12Z BERMUDA UPPER-AIR OBSERVATION
OF 10 KT NORTHEAST WIND AND 5940 METER HEIGHT. THIS OBSERVATION
SUGGESTS THAT THE RIDGE TO THE NORTH OF BERMUDA AND ISABEL EXTENDS
SOUTHWESTWARD FARTHER THAN THOSE FOUR MODELS ARE INDICATING. MORE
RIDGING WOULD SUGGEST THAT...AT LEAST IN THE SHORT TERM... ISABEL
SHOULD MOVE FARTHER WEST THAN THESE MODELS ARE FORECASTING BEFORE
THE HURRICANE BEGINS TO TURN NORTHWESTWARD. ONLY THE NOGAPS MODEL
INITIALIZED THE 500 MB PROPERLY TO THE BERMUDA OBSERVATION...AND
THE 12Z NOGAPS TRACK IS TO THE LEFT OR WEST OF THE PREVIOUS AND
CURRENT FORECAST TRACKS. THE OFFICIAL FORECAST TRACK IS JUST AN
EXTENSION OF THE PREVIOUS TRACK AND IS A LITTLE TO THE WEST AND
SLIGHTLY FASTER THAN THE MODEL CONSENSUS. THERE REMAINS SOME
UNCERTAINTY ON WHERE THE EXACT LANDFALL OF ISABEL COULD OCCUR SINCE
THE DEVELOPING CENTRAL U.S. TROUGH COULD STILL DEEPEN AND DIG MORE
SOUTHWARD THAN THE MODELS ARE INDICATING. THIS COULD INDUCE A MORE
NORTHWARD MOTION AND RESULT IN LANDFALL FARTHER UP THE U.S. EAST
COAST. BUT AS IN THE PREVIOUS SEVERAL MODEL RUNS...A LARGE AND VERY
STRONG NORTH-SOUTH ORIENTED RIDGE IS FORECAST TO REMAIN EAST OF
ISABEL AND PREVENT THE HURRICANE FROM RECURVING NORTHEASTWARD.
ONLY MINOR FLUCTUATIONS IN INTENSITY ARE EXPECTED FOR THE NEXT
COUPLE OF DAYS AS ISABEL IS FORECAST TO MOVE OVER SIGHTLY WARMER
WATER AND REMAIN IN A FAVORABLE UPPER-LEVEL OUTFLOW PATTERN. BY 96
HOURS...ISABEL IS FORECAST TO BEGIN ACCELERATING NORTH OR
NORTH-NORTHWESTWARD UNDER INCREASING SOUTHERLY UPPER-LEVEL FLOW.
HOWEVER...THE CENTRAL CORE OF ISABEL IS EXPECTED TO REMAIN EAST OF
THE STRONGEST WINDS AND UNDER 15-25 KT 200 MB FLOW. THIS WOULD TEND
TO KEEP ISABEL STRONGER THAN WHAT THE SHIPS INTENSITY MODEL HAS
BEEN INDICATING...ESPECIALLY SINCE ISABEL WILL BE MOVING OVER THE
WARM GULFSTREAM OFFSHORE NORTH CAROLINA JUST PRIOR TO LANDFALL.
FORECASTER STEWART
FORECAST POSITIONS AND MAX WINDS
INITIAL 14/2100Z 24.1N 67.4W 135 KT
12HR VT 15/0600Z 24.7N 68.9W 135 KT
24HR VT 15/1800Z 25.7N 70.2W 135 KT
36HR VT 16/0600Z 26.7N 71.3W 130 KT
48HR VT 16/1800Z 28.0N 72.2W 125 KT
72HR VT 17/1800Z 31.2N 74.0W 120 KT
96HR VT 18/1800Z 36.5N 76.0W 105 KT
120HR VT 19/1800Z 43.5N 78.0W 35 KT...INLAND
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